The correlation between mixing length and metallicity on the giant branch: implications for ages in the Gaia Era

Jamie Tayar, Garrett Somers, Marc H. Pinsonneault, Dennis Stello, Alexey Mints, Jennifer A. Johnson, O. Zamora, D. A. García-Hernández, Claudia Maraston, Aldo Serenelli, Carlos Allende Prieto, Fabienne A. Bastien, Sarbani Basu, J. C. Bird, R. E. Cohen, Katia Cunha, Yvonne Elsworth, Rafael A. García, Leo Girardi, Saskia HekkerJon Holtzman, Daniel Huber, Savita Mathur, Szabolcs Mészáros, B. Mosser, Matthew Shetrone, Victor Silva Aguirre, Keivan Stassun, Guy S. Stringfellow, Gail Zasowski, A. Roman-Lopes

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In the updated APOGEE-Kepler catalog, we have asteroseismic and spectroscopic data for over 3000 first ascent red giants. Given the size and accuracy of this sample, these data offer an unprecedented test of the accuracy of stellar models on the post-main-sequence. When we compare these data to theoretical predictions, we find a metallicity dependent temperature offset with a slope of around 100 K per dex in metallicity. We find that this effect is present in all model grids tested, and that theoretical uncertainties in the models, correlated spectroscopic errors, and shifts in the asteroseismic mass scale are insufficient to explain this effect. Stellar models can be brought into agreement with the data if a metallicity-dependent convective mixing length is used, with Δα ML,YREC ~ 0.2 per dex in metallicity, a trend inconsistent with the predictions of three-dimensional stellar convection simulations. If this effect is not taken into account, isochrone ages for red giants from the Gaia data will be off by as much as a factor of two even at modest deviations from solar metallicity ([Fe/H] = −0.5).
Original languageEnglish
Article number17
JournalThe Astrophysical Journal
Issue number1
Publication statusPublished - 28 Apr 2017


  • astro-ph.SR


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